1. Field of the Invention
This invention relates generally to exhalation valves as used in patient respiratory systems and more particularly to noise reducing techniques in these respiratory systems.
2. Description of the Prior Art
The basic types of prior art exhalation valves and their diaphragms are well-known. These exhalation valves have been in use for many years and have met their special needs as presented by specific problems and have thus generally served narrow purposes. Some of these prior art devices have been described in the following listed patents, which were brought to the attention of the Applicant's attorney through a novelty search conducted in the United States Patent and Trademark Office:
______________________________________ Number Title Inventor ______________________________________ 2,705,608 Non-Chattering Pilot Controlled G. M. Phillips Diaphragm Valve 3,559,676 Antihunting Diaphragm Valves L. D. Haskins 3,584,621 Respiratory Apparatus F. M. Bird 3,608,574 Diaphragm-Valve Especially for R. Beaussant a Respiratory-Gas Supply System 3,822,819 Fastener Driving Tool with S. Wilson et al Improved Valve 3,861,642 Fluid Control Valve G. E. Maddocks ______________________________________
Many of these prior art devices have defects which render them inoperable with some respiratory systems. For example, some flow rate measurement systems are sensitive to acoustic disturbances and the measurements obtained under conditions including disturbances of this type are unreliable. Prior art exhalation valves used in respiratory therapy equipment generally have generated a wide spectrum of acoustical noise during the period when the patient exhales past a conventional partially pressurized exhalation valve diaphragm. Two or more frequencies of this spectrum may be amplified by components of the patient respiratory system to the point that they become objectionable in the form of annoying sound to the patient and disruption of the measuring processes of acoustically sensitive instruments, for example, vortex counting acoustic flowmeters.
Examples of major acoustic disturbances include an audible mid-range honk or moaning sound caused by sympathetic vibrations between associated tubing and the exhalation valve diaphragm, typically a very thin membrane, as it bows and stretches in response to pressure fluctuations upstream of the valve. Another disturbance manifests itself as a high frequency squeal that usually occurs at low flow rates and represents harmonic oscillations of an airspace in the valve as it is disturbed by a thin sheet of high velocity air issuing from the valve.
It would thus be a great advantage to the art to provide an exhalation valve for use in a patient respiratory system that neither generates nor propagates acoustic disturbances.
It would be a specific advantage to the art to provide such an exhalation valve that presents no annoying sounds to the patient.
It would be a further specific advantage to the art to eliminate disruptive acoustical disturbances to measuring instruments used in patient respiratory systems.